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What are ADSL VCI/VPI and what to use ?

A DSL modem needs to have the Virtual Path Identifier (VPI) and Virtual Circuit Identifier (VCI) set in order to work correctly. In essence, these two numbers tell the DSL equipment on both ends that they should talk to each other, you can think of them as having a similar functionality to dialing a number on a regular phone line. Each DSL provider uses a set of these two numbers.

Bellow is the actual technical definition of both:

VPI (Virtual Path Identifier) is an eight-bit field in an ATM cell's header that identifies the virtual path (a bundle of virtual channels that have the same endpoint) to which the cell belongs as it travels through an ATM network.

VCI (Virtual Channel Identifier) is a 16-bit field in an ATM cell's header that identifies the cell's next destination as it travels through an ATM network (similar to Frame Relay's DLCI). A virtual channel is a logical connection between two end devices on an ATM network.

An ATM switch uses either the VPI, VCI, or a combination of both to route the cell to its destination.

For a list of known VCI/VPI values, please see this article.

Please note that some ISP's (Earthlink, Mindspring, Speakeasy, etc.) may use your local telco for the network services. In such cases, just use the VPI/VCI values for your telco/CLEC.

  User Reviews/Comments:
by anonymous - 2016-02-17 15:59
I've been told that actually you can only ever connect one phone line to one DSL provider. That makes VPI/VCI not really make sense - why do you need to dial a number, on a phone that can only call one person?
by Philip - 2016-02-17 18:52
The key here is that they are "virtual" constructs... They are simply parts of the cell header that help identify a virtual channel between end points, not a physical one.
by anonymous - 2017-07-18 13:00
The VPI/VCI can be used to offer different services. The VPI/VCI is part of the ATM Protocol used by ADSL networks . As an example a network provider that offers residential internet services and IPTV services or other special services over the same physical link may use different vpi / vci for each service to route the traffic differently though the core network.
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